Problem: Which of these numbers is composite? ${11,\ 15,\ 19,\ 41,\ 83}$
A composite number is a number that has more than two factors (including 1 and itself). 11, 19, 41, and 83 each have only two factors. The factors of 15 are 1, 3, 5, and 15. Thus, 15 is the composite number.